This invention relates to improvements in the construction and operation of cranes for moving cargo between a dock and a ship.
Recent decades have seen major changes in the handling of seagoing cargo. The most notable development in this respect has been the evolution and utilization of container ships and container cranes. Container ships are configured and equipped to carry their cargo in large rectangular containers which have standarized dimensions facilitating their stacking and handling. A typical container crane is a large quayside gantry crane, movable lengthwise on the dock on railroad-like rails. The crane has a large horizontal beam which extends over a ship moored alongside a dock. A horizontally movable carriage or trolley rides on the horizontal beam, and wire ropes on the trolley suspend a spreader which is designed to engage the upper regions of containers. Such engagement may be made by means of twist lock mechanisms, examples of which are disclosed in Loomis et al U.S. Pat. No. 3,749,438. The trolley is operated to carry cargo the entire vertical and horizontal distances between the dock and the ship.
A shortcoming of the typical container crane described above is that, due to the distances the containers must travel, the cycle time is too long. Operating the trolley at a higher velocity is helpful but it cannot, as a practical matter, provide a major increase in the per hour capacity of the crane. Realizing this situation, others have proposed the utilization of two different cargo moving devices on the crane, arranged to handle the containers in series somewhat like the bucket brigades in which volunteer fire fighters passed pails of water forwardly from hand-to-hand. Examples of cargo cranes using these principles are described in the following patents:
______________________________________ Australian patent 87428 U.S. Pat. No. Inventor 3,812,987 Watatani 4,018,349 Hupkes 4,046,265 Wormmeester et al 4,172,685 Nabeshima et al 4,293,077 Makino. ______________________________________
In the system disclosed in the Australian patent, there is an elevating platform, but it is served by only one trolley. The systems shown in most of the other listed patents have two trolleys which service a landing platform which is located at a fixed height. It is believed that none of these prior systems is capable of the performance of the present invention, with respect to the reduction of cycle time, and the reduction of distances between the operators and the locations where container movements are made at the ends of container travel.